1. Field of the Invention
The present invention relates to a multi-layer circuit board formed by laminating and bonding plural resin films and a method of manufacturing the same.
2. Description of Related Art
An example of a method of manufacturing a multi-layer circuit board is shown in JP-A-2000-38464. An essence of a method of preparing a resin film with a circuit pattern in the manufacturing method is illustrated in FIGS. 6A-6G attached hereto. As shown in FIG. 6A, a copper foil 2 is pasted to a resin film 1 which is made of thermoplastic resin such as liquid crystal polymer (LCP). Then, as shown in FIG. 6B, a resist 3 is coated on the copper foil 2, and the coated resist 3 is covered with a photo-mask 4. A circuit pattern is developed on the copper foil 2 after it is exposed to light. Then, as shown in FIG. 6C, the copper foil 2 is etched, and the copper foil 2 other than the circuit pattern is removed. Then, as shown in FIG. 6D, the resist 3 covering the circuit pattern is removed, thus forming a resin film 10 with a circuit pattern.
As shown in FIG. 6E, both surfaces of the resin film 1 on which a circuit pattern is formed are covered with protecting films 5. Then, dead-ended holes 6 are formed through the resin film 1 and the bottom protecting film 5 by radiating a laser beam. Then, as shown in FIG. 6F, the dead-ended holes 6 are filled with conductive paste 7. Finally, the protecting films 5 are removed, thus forming a resin film 10 having the circuit pattern and the dead-ended holes 6 filled with conductive paste 7.
According to the method disclosed in JP-A-2000-38464, a plurality of resin films 10 thus made are laminated and bonded together by pressurizing the laminated resin films 10 under heat. At the same time, the conductive paste 7 is sintered, thereby forming conductors electrically connecting neighboring circuit patterns.
In the conventional method, as shown in FIGS. 6A-6G, the circuit pattern is formed under a wet process, i.e., a photolithography process. Therefore, the number of steps included in the process of forming the circuit pattern is considerably large, and the wet process is complex. Further, many photo-masks 4 are required for forming the circuit patterns on each layer constituting a multi-layer circuit board. In addition, the circuit pattern is formed from a relatively thick copper foil 2. Therefore, a fine circuit pattern in a high density cannot be made.